We have, in earlier chapters in this book, explicitly discussed the concept of the capacity of a cellular system. In particular, in Chapter 2 we used the well-known Erlang-B formula to relate the blocking probability of a call attempt to traffic intensity (the call arrival rate times the call holding time) and the capacity, in number of channels, each capable of handling one call. In Chapter 3, we showed how the introduction of the cellular concept increased the overall system capacity, in terms of the number of simultaneous calls that could be handled. We further showed in Chapter 4 that Dynamic Channel Assignment, DCA, could, in principle, be used to increase system capacity for the case of moderate traffic intensity. In Chapter 6 we then compared the capacity of three second-generation digital cellular systems, IS-136, IS-95, and GSM. In that chapter we noted as well that mobile calls had to be handed off to adjacent cells as mobiles moved through a specified system. In particular, we noted that the CDMA-based IS-95 offered an improved performance because of the possibility of using soft handoff. We followed up on this introduction to handoffs by commenting on the actual process of handoff in Chapter 8.

In this chapter we quantify our discussion of the handoff process by describing cellular admission control: new call attempts are accepted in a given cell only if capacity is available to handle the call. Otherwise the call attempt is blocked.